Android: How can I port ExecuteScalar to Java?

问题

SqlCommand.ExecuteScalar Method
Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

I guess this will involve heavy use of generics.

Assume I have an SQLiteDatabase/Cursor object.

回答1:

Have a look at SQLLiteStatement

long simpleQueryForLong() Execute a statement that returns a 1 by 1 table with a numeric value.

String simpleQueryForString() Execute a statement that returns a 1 by 1 table with a text value.

回答2:

This logic worked for me:

public int ExecuteScalar(/* code...*/) {
    Cursor cursor = database.rawQuery(sql, selectionArgs);
    try {
        cursor.moveToNext();
        int val = cursor.getInt(0);
        cursor.close();
        return val;
    }   
    catch (Exception e) {
        /* code...*/
    }
    return -1;
}

回答3:

If you're retrieving a primary key then you can use the statement getGeneratedKeys method which returns a resultSet of generated keys after an insert.

回答4:

Giving the database object is db

long result = db.compileStatement("select count(*) from some_table").simpleQueryForLong();

来源：https://stackoverflow.com/questions/7348644/android-how-can-i-port-executescalar-to-java